1. Field of the Invention
The present invention concerns a method and device for transmitting and switching packets in an optical network.
2. Description of Related Art
The monomode optical fiber is increasingly being used in telecommunications networks. In the near future, it is probable that the user shall have direct access to the monomode fiber. From now on, the capacity continuity of the channel between any two subscribers shall be effective. The costs of optical transmitters and receivers scarcely depend on the information rate. Thus, it is possible to envisage modulating the extremely high rate sources and fix the capacity of a channel by the occupation time determined by the ratio between the period of the packet and the time separating two successive packets.
But the introduction of optics in the functions of the network is currently adversely affecting the structure of Asynchronous Transfer Mode (ATM) and SDH time-division signals where these functions accompany highly elaborate management and processing devices beyond the range of optics.
An article by J. P. Coudreuse, G. Pays and M. Trouvat and entitled the asynchronous time-division technique (Switching and Transmission, No 3, 1990) describes the Asynchronous Transfer Mode (ATM) which is defined to satisfy three criteria; digital technique, high rate and flexibility. This is a hybrid technique between the switching of circuits for which it retains simplicity (gauge of extremely high rates) and the switching of packets for which it assumes flexibility. This is the culmination of various convergent and intermediate evolutions which became operational over the last few years; rapid switching of circuits so as to attempt to resolve the switching of huge amounts of information and the rapid switching of packets to increase the processed rate by simplifying the protocol layers (frame switching, frame relaying).
The difficulty of introducing optics into the other functions of the network paradoxically results in its success in transmission. In fact, the reduction of the cost of the telephone channel each time the rate rises, together with the extremely large passband of the fiber, have caused transmission systems to be developed even faster. It is nevertheless another approach to increase the capacity of an optical network, one which favors the parallelism of circuits in a given optical conduit by wavelength multiplexing. This approach, still deferred on transmission for cost reasons, shall shortly be used for direct detection systems with rates of 10 Gbit/s, indeed more, where the limits of the monomode fiber are reached.
An article by H. Paciullo entitled "Multicolored optical networks" (Echo des Recherches, No 146, 4th quarter 1991) defines the concept of multicolored networks. These multicolored networks are mainly characterized by the fact that they use a large number of wavelengths or optical frequencies for embodying communication networks. This concept has been able to be developed owing to the emergence of the monomode optical fiber which has an extremely large passband (several thousands of gigahertz in the third window around 1.5 .mu.m) and by the development in a laboratory of new optical and optoelectronic components. The main originality of these techniques resides, not merely in the quantitative aspect (capacity of networks having nothing in common with those currently existing), but also in the fact that in this instance the wavelength may be regarded as a network element and that accordingly network operating and management functions may be directly applied to all the wavelengths.
The multicolored optical networks offer an original solution to the ever-increasing needs of networks in terms of capacity. However, they require sophisticated optical components, some of the latter still being at the research stage and this is why this type of network is not currently being exploited commercially.
These arguments concerning costs are to be reconsidered before fully organizing a network. The coherent detection systems have resulted in proposals for organizing a multicolored network. However, technological immaturity has prevented this network from being produced.
The object of the present invention is to provide a new organization of the functions of an optical network able to mitigate these various drawbacks.